How can I reset Physics for fluid simulation?
Regular physics Collision has no effect on liquids. If you are using correct Fluid Collision, check that the normals are the right way on your plane.
Because the mesh of a fluid domain is actually completely replaced by the mesh generated by the simulation, the domain itself always must be cuboidal and aligned with the world axes and will thus will automatically be a bounding box of whatever mesh the domain was originally,
To clear the cache of a fluid domain: Seek to scene frame 1, then force the fluid cache to delete by changing the domain resolution, then change it back. The cache will reset unless you baked it.